The G-14 is heavier, but has a far more powerful engine. It will thus flat turn somewhat worse than the G-2 (about 5% larger turning radius), but is about 20mph faster at usual AH altitudes (over 20k the G-2 is actually slightly faster). The biggest difference is probably in climb rate, up to about 16k the G-14 adds some 500ft/min to the G-2 already top-notch rate of climb.
This additional power comes at a price, the torque effects are much bigger and more pronounced than in the G-2. Spoken in common terms, you give up some nimbleness and flat turn performance for some additional nose-up performance and a better ability to catch runners.
And of course, there is an increase in firepower by substituting the 7.9mm machineguns with 13mm ones.